Go with a polymer modified thinset, plywood will eventually rot so I would skip it in favor of a thicker cement board. make sure the tile can withstand extreme temperature fluctuations. (I'm sure NY doesn't get too cold, but if you put a hot dish on a cool tile, it may crack.) Any kind of tile adhesive will eventually let go in an outdoor situation. Definitely grout your joints. I prefer sanded grout for ease of use, but the pro's say if you are doing a 3/16 or smaller joint use unsanded grout.
Over budget and behind schedule...
That's how I roll :)
Last edited by Daddytron; 03-26-2012 at 05:45 PM.